Inclusion Criteria:

• Appropriate written assent is obtained from the patient and written informed consent is obtained from the parent or legal guardian (defined by the IEC/IRB)
• A boy or girl aged 6 through 16 years (at the start of the previous double blind study), inclusive, who participated in study C1538/3027/NA/MN or C1538/3028/AP/MN
• Have a diagnosis (as established in the previous double blind study) of narcolepsy (or presumed narcolepsy) or OSAHS according to the criteria established by the International Classification of Sleep Disorders (ICSD) manual of the American Academy of Sleep Medicine (AASM)
• Continue to be in good health as determined by a medical and psychiatric history, ECGs, physical examination findings, serum chemistry, hematology, and urinalysis
• Have blood pressure values greater than those for the 5th percentile and less than the 95th percentile on the National High Blood Pressure Education Program guidelines for blood pressure levels for boys and girls ages 6 through 16 years
• Girls who are post menarche or sexually active who have a negative urine pregnancy test at the screening/baseline visit, must be using a medically acceptable method of birth control, and must agree to continued use of this method for the duration of the study (and for 30 days after participation in the study). Acceptable methods of birth control include: barrier method with spermicide; steroidal contraceptives (oral, topical [patch], implanted, and injected) in conjunction with a barrier method; intrauterine device (IUD); or abstinence
• No positive urine drug screen (UDS) for any illicit drug or alcohol (ethanol) at baseline visit, unless a false positive is suspected, in which case the UDS will be repeated. If the patient has a positive drug screen for methylphenidate or amphetamine at screening, the patient must have a negative UDS after a washout period and prior to baseline.
• Have a parent or legal guardian who is willing to participate in the study
• Continue to meet inclusion criteria from the previous study, as appropriate

Exclusion Criteria:

• Have self induced sleep deprivation/poor sleep hygiene
• Have a past or present seizure disorder (except history of a single febrile seizure), a history of psychosis, or of clinically significant head trauma (eg, brain damage) or past neurosurgery
• Have a history of suicide attempt, or are at suicidal risk
• A clinically significant drug sensitivity to stimulants such as amphetamine, dextroamphetamine, methylphenidate, or pemoline; and modafinil or any of its components
• Any disorder that could interfere with drug absorption, distribution, metabolism, or excretion (including previous gastrointestinal surgery)
• Active, clinically significant gastrointestinal, cardiovascular, hepatic, renal, hematologic, neoplastic, endocrine, neurologic, immunodeficiency, pulmonary, or other major clinically significant disorder/disease
• Any clinically significant deviation from the normal range(s) in the ECG or physical examination findings, or clinical laboratory (ie, hematology, serum chemistry, urinalysis) test results at the screening/baseline visit
• Absolute neutrophil count (ANC) below the lower limit of normal at the baseline visit (NOTE: If the ANC is below the lower limit of normal at the baseline visit, the medical monitor will be consulted for continued eligibility in the study.)
• A seated pulse outside the range of 60 through 115 bpm after resting for 5 minutes
• A total daily intake of more than 500 mg of caffeine per day (eg, approximately ten 12 ounce caffeinated sodas, 5 cups of coffee or tea, or about 25 ounces of chocolate per day) within 1 week of the baseline visit
• Pregnant or lactating/nursing; any child who becomes pregnant during the study will be withdrawn.